The
Archaea may be the oldest
life forms on earth. They are
prokaryotes.

It is believed
that the archaea may be the
oldest life forms on earth, and that the
bacteria and eukaryotes have
evolved from them and with them, at least
in part. The
relationships are still being studied,
and right now the scientists think that perhaps the
early archaea and bacteria may have been
the survivors of a pool of life forms that
were all in the early stages of their
evolution. There may have been informal DNA
(information) sharing in this pool, and organisms in
each of the three domains share some DNA
present in the other two.

The Archaea have only recently been
recognized as members of a separate domain.
The members of the archaea are tiny
prokaryotes that look a lot like
bacteria, and, until Dr. Carl Woese at
the University of Illinois started
studying their DNA sequences, no one had
guessed that these little prokayrotes were
a separate group of living things.

Many of the archaea live in very
challenging environments, which are
perhaps similar to the environments on
the early earth. These hardy
little organisms are called
extremeophiles (because they like
extreme conditions). Recent
widespread interest in extremeophiles
pursues several lines of inquiry:

How,
and under what conditions, did life
begin on earth ?

What are the
environmental limits which make the
development of life possible or
impossible?

How
do archaea work, biochemicaly and
structurally?

How
are archea related to other life
forms on earth?

How
can more of these organisms be
cultured in the laboratory?

The space program, which has gathered so
much information about our solar system,
has also stimulated a lot of curiosity
about whether or not there is life
"out there". NASA, and
some universities, have begun the study
of Astrobiology, and their scientists
are naturally very interested in these
extremophiles.

Archaea
have also been found floating amid the
plankton in the open ocean and in hot,
geothermally heated water under
ground. Others have been found in
places that we would consider normal for
living beings. Not all archaea are extremeophiles.
They are amazingly adaptable organisms.

Here is an interesting idea for you,
which I came across in the book Rare
Earth:

Complex life forms
(animals and plants) adapt morphologically,
which means that they change the shapes
of their bodies and modify their
physical systems..

An organism which is only one cell can
make changes in its internal chemistry,
and can experiment with its chemical
processes and how it uses its amino
acids.

However,
these kinds of changes are impossible for a
multicellular animal or plant to
make. The way
that its cells work together make
fundamental chemical changes too
disruptive to be practical. These complex
organisms can change their sizes, the
shapes of their bodies and limbs, how
they manage body heat, and how they deal
with hormones and supplies of water and
food.

Thinking about this, it makes sense that
the basic chemical plan of a life form has to be laid
out fairly early in the evolutionary
process. What sorts of animals and
plants might develop in an environment
that was different from ours?
Given lots of time, could some of these
extremeophiles evolve into
complex life forms that are very
different ones we know?